Reaction During the Sputtering of Metals onto Polyimide - ACS

Chapter 20

Reaction During the Sputtering of Metals onto Polyimide 1

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A. Domingue , L. Dignard-Bailey , Edward Sacher , A. Yelon , and T. H. Ellis 2

Downloaded by UNIV LAVAL on July 11, 2014 | http://pubs.acs.org Publication Date: November 9, 1990 | doi: 10.1021/bk-1990-0440.ch020

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Groupe des Couches Minces and Département de Génie Physique, École Polytechnique, C.P. 6079, Succursale A, Montreal, Quebec H3C 3A7, Canada Département de Chimie, Université de Montréal, C.P. 6128, Succursale A, Montreal, Quebec H3C 3J7, Canada

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X-ray photoelectron spectroscopy has been used to study the metal polyimide interface formed during room temperature metal deposition. Several monolayers of Al, Au and Cu were sputter-deposited onto cured polyimide, to a thickness which permitted the observation of both polyimide and metal peaks. Deconvolution of core-level Cls, Nls and Ols polyimide peaks and Al2p, Au4f and Cu2p metal overlayer peaks has demonstrated that chemical reaction occurs at the carbonyl sites for a l l these metals under the conditions used. In addition, the aromatic nature of the molecular structure at the interface is believed to decrease while the percentage of an isoimide-like component increases. 3/2

The polyimides, unusually strong, versatile and stable insulating polymers, have acquired increasingly important roles in the thin film industry as high performance material coatings and dielectric layers necessary for the demanding conditions experienced by special high technology devices such as multilayer microelectronic structures (1-4). The long term mechanical stability of such devices depends greatly on the adhesion experienced at the metal-polymer interface and, as a result, the development of a metal-polyimide interface with enhanced stability and reliability has become an important industrial objective. Interfacial adhesion had been previously believed to be a consequence of a combination of mechanical intermixing, interfacial mixing of phases and intrinsic effects at the interface (5-7). The depth-profile characteristics of the metal-polyimide interface have been shown, in fact, to vary with the vapor-deposited metal utilized; however, this has not been sufficient to justify the amount of interfacial adhesion actually observed (8). There are also specific interfacial interactions, a 3

Current address: Metals Technology Laboratories, Canada Centre for Minerals & Energy Technology, Ottawa, Ontario K1A 0G1, Canada 0097-^156/90/0440-0272$06.00/0 © 1990 American Chemical Society In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


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consequence o f the i n t r i n s i c properties of the interface, which are strongly implicated and they influence the d u r a b i l i t y and strength of adhesion. Of these interactions (chemical, e l e c t r o s t a t i c and molecular), i t i s the presence of chemical bonds a t the interface, providing the strongest adhesive l i n k s , which are best suited to withstand current processing techniques (3., 9) . In order to monitor the progress of i n t e r f a c i a l reactions occurring during the m e t a l l i z a t i o n of cured polyimide, x-ray photoemission spectroscopy (XPS or ESCA) was used to reveal e l e c t r o n i c core-levels i n d i c a t i v e of the environment at the interface and adjacent regions. Evidence of chemical reaction would include the appearance of new peaks with c h a r a c t e r i s t i c binding energies (chemical s h i f t s ) representative of new or a l t e r e d chemical states o f the element. We can thus ascertain the formation of metal-oxygen chelate complexes (1). Previous studies have shown that a trend exists i n the behavior of some evaporated metals on polyimide surfaces: x-ray and u l t r a v i o l e t photoelectron (XPS, UPS) as w e l l as high r e s o l u t i o n electron energy loss (HREELS) measurements have indicated that while f o r some metals such as aluminum, titanium and chromium there i s bond formation with the PMDA carbonyl oxygen of the polyimide (2, 10-13), other metals such as copper, palladium and gold undergo l i t t l e reaction or i n t e r a c t i o n (10,12,14,15). I t has, however, since been postulated that metals, i n order to adhere w e l l at a l l to a polymer under a wide v a r i e t y of conditions, must form metal- polymer bonds (10). Deposition of metals can proceed v i a thermal evaporation which produces low energy vaporized atoms which condense onto the sample surface. The heat of condensation liberated, 300 - 450 kJ per mole (!U»1Z), Is high enough f o r reaction to occur between metal and polymer (18) but i s r e s t r i c t e d to those metal species which are the most h i g h l y reactive; analysis of i n t e r f a c i a l species i n the l i t e r a t u r e i s minimal. In contrast to evaporation, sputter-deposited "hot" metal atoms have s i g n i f i c a n t l y higher average energies (at l e a s t ten times greater (18), which r e s u l t s i n more extensive i n t e r f a c i a l reaction (1) and, thus, produces more c l e a r l y measurable changes, as observed i n t h i s study. The p o t e n t i a l l y damaging e f f e c t s of s i g n i f i c a n t substrate heating during sputter-deposition are minimized by using low deposition rates (19). The s u b s t a n t i a l l y increased adhesion obtained with sputter-deposited metal-polymer interfaces has resulted i n the growing importance of metal sputtering f o r the deposition of t h i n metal films on polymers (1). EXPERIMENTAL Core l e v e l spectra were acquired i n a Vacuum Generators dual chamber UHV system. This consists of the ESCALAB Mk II electron spectrometer run by the SURFSOFT data a c q u i s i t i o n and manipulation program (20) on an AT-type microcomputer, an analyzer chamber f o r taking the measurements and a preparation chamber f o r sample introduction and treatment. The samples were transferred d i r e c t l y from the preparation chamber to the analysis chamber. The data were obtained with the analyzer operating at 20 eV pass energy i n the constant analyzer energy mode, using non-monochromatized Mg Κα (1253.6 eV) r a d i a t i o n . The experimental resolution was 0.80 eV FWHM. Operating

In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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METALLIZATION OF POLYMERS 10

pressures i n the analysis chamber never exceeded 5 χ 1 0 " t o r r . The system possesses an argon ion gun f a c i l i t y f o r sample cleaning and sputtering, and has p r o v i s i o n f o r sample heating i n vacuo. Metal depositions were c a r r i e d out i n the preparation chamber by bombarding the metal targets with 6 kV (for Al) and 3 kV (for Au and Cu) argon ions a t a background pressure of 5 χ 10" t o r r . The samples were positioned on the transfer system r a i l i n g at some distance from the metal target and well out of the way of the sputter beam (preliminary studies showed no detectable degradation of the samples by the beam at t h i s p o s i t i o n ) . Such conditions r e s u l t e d i n metal f i l m deposition thicknesses of approximately 20 Â a f t e r 30 minutes. The metals used (Al, Au, Cu) were of 99.99% p u r i t y ( A l f a ) . A l l gases used were o f u l t r a high p u r i t y (Linde). The polyimide t h i n f i l m samples wre prepared by spin coating an approximately 2 μα. f i l m of e l e c t r o n i c grade PMDA-ODA polyamic a c i d precursor (Dupont PI-2545) onto a 3" s i l i c o n wafer. This f i l m was d r i e d under vacuum at 85 °C f o r several hours and cured at 350 °C i n the preparation chamber f o r 30 minutes. Reactions occurring at the interface during sputtering were monitored using the Cls, 01s, Nls and appropriate metal e l e c t r o n i c core l e v e l s (21-24). Analysis was c a r r i e d out a t 85° from normal (grazing angle), thereby probing the core l e v e l s at the i n t e r f a c e . A f t e r background subtraction ( S h i r l e y ) , the core l e v e l spectra were f i t with 70% Gaussian, 30% Lorentzian peaks i n order to h i g h l i g h t the various contributions. There was only a s l i g h t charge-induced s p e c t r a l s h i f t f o r the t h i n f i l m samples and t h i s was r e a d i l y compensated f o r by referencing the polyimide aromatic peak to -285.0 eV binding energy.


6

RESULTS AND DISCUSSION POLYIMIDE. The XPS spectra of t h i n films of clean, cured PMDA-ODA polyimide (Fig. 1), examined p r i o r to metal deposition, display core l e v e l contributions and peak i n t e n s i t y r a t i o s i n agreement with those generally observed f o r the cured polyimide film surfaces (21,25) (Figs. 2a-c and Table I ) . The r e l a t i v e contributions from the major carbon Is peaks (Fig. 2a) representing the various components o f the PMDA-ODA polymer repeat unit, conform to previous assignments (25) and include the PMDA imide carbonyl carbon peak (peak 2) , the peak representing the ODA aromatic r i n g carbons not bound to oxygen or nitrogen (peak 4), the peak representing unresolved contributions from remaining carbons i n the structure (peak 3) and the broad aromatic π - π* shake-up contributions (peak 1). The small extra peak, observed a t lower binding energy (peak 5), i s generally not accounted f o r (except as a peak asymmetry) (21) and we s h a l l not elaborate on i t i n t h i s discussion. These are a l l i n excellent agreement with the l i t e r a t u r e (25). The relative contributions o f the major oxygen Is peaks (Fig. 2b) o r i g i n a t i n g from the ether (peak 1) and carbonyl oxygens (peak 2) demonstrate the non-stoichiometric nature of cured polyimide f i l m surfaces evident i n a carbonyl-ether r a t i o of less than the 4:1 r a t i o t h e o r e t i c a l l y expected (21,25,26). A t h i r d , very weak peak at lower energy i s not i d e n t i f i e d . The Nls spectrum ( F i g . 2c) i s , c h a r a c t e r i s t i c a l l y , dominated by the band corresponding to the imide nitrogen (peak 2). I t also displays a small u n i d e n t i f i e d peak at


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Sputtering ofMetals

Table I. Cured Polyimide Film

Position/Shift Spectrum

Peak

(exptl)

%Area

Origin

(theor.)

-291.5/-6.5 +289.1/-4.1 -286.1/-1.1

3.7 11.0 49.3

4 5

-285.0/ 0.0 -283.4/+1.6

34.9 1.1

36.4

01s

1 2 3

-533.7/-1.3 -532.4/ 0.0 -530.7/+1.7

29. 68. 2.

20.0 80.0

ether carbonyl

Nls

1 2 3

-402.7/-1.7 -401.0/ 0.0 -399.3/+1.7

4. 91. 3.

100.0

imide isoimide

Cls


(eV)

%Area

7Γ-7Γ

18.2 45.4

c=o C-0 C-N C-C=0 aromatic

higher binding energy (peak 1) , as well as a lower energy component (peak 3) not accounted f o r i n the bulk structure but generally believed to be due to the presence of isoimide structures (25) ; t h i s s t r u c t u r a l isomer of polyimide i s generally believed to be the reason f o r the carbonyl deficiency observed (22,2.5) . ALUMINUM. A chemical reaction i s known to occur when aluminum i s deposited v i a evaporation onto polyimide (27)· Sputter-deposition produces s i m i l a r e f f e c t s on the core l e v e l s (Figs. 3a-c, 4a) (Table I I ) . This includes a s i g n i f i c a n t reduction of the carbonyl Cls peak i n t e n s i t y (peak 2 i n F i g . 3a) and reduction the 01s carbonyl peak i n t e n s i t y (peak 2 i n F i g . 3b). This i s generally explained as a consequence o f the s e l e c t i v e reaction occurring at the carbonyl s i t e s a t the surfaces (14,28). The l i m i t e d nature o f the reaction, p o s s i b l y due to changes i n s i t e a c t i v i t y (13), i s underlined by the reduction i n Cls carbonyl peak i n t e n s i t y which does not exceed approximately 50% o f the o r i g i n a l s i g n a l (peak 2 i n F i g . 3a). This agrees with the suggestion that only one h a l f of the carbonyls available undergo reaction with aluminum atoms (10). There i s also a reduction i n the Cls π - π* contribution (peak 1 i n F i g . 3a) which can be a t t r i b u t e d to a reduction i n electron d e r e a l i z a t i o n i n the PMDA or ODA structures (loss of aromatic character). The other carbon peaks maintain t h e i r r e l a t i v e i n t e n s i t i e s , however, and t h i s shows that the polyimide structure i s generally retained a f t e r sputter-deposition of the aluminum. The presence of any carbides, t y p i c a l l y e x h i b i t i n g Cls binding energy peaks below 284 eV, can possibly account f o r peak 5 i n F i g . 2a but the absence of a concurrent high energy carbide peak (-79.8 eV) (29) i n the Al2p core l e v e l spectrum (Fig. 4a) precludes t h i s p o s s i b i l i t y . There appear to



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METALLIZATION OF POLYMERS

F i g . 1: PMDA-ODA polyimide repeat unit.

Binding Energy (eV)

Fig. 2a: XPS spectra of cured polyimide film: C Is spectrum.


Sputtering of Metals


20. DOMINGUEETAL.

Binding Energy (eV)

Fig. 2c: XPS spectra of cured polyimidefilm:Ν Is spectrum.


in

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Table I I . Aluminum on Polyimide

Spectrum Cls

Peak

Position/Shift (eV)

%Area

Origin

1 2 3

-291.3/-6.3 -289.0/-4.0 -285.9/-0.9

1.0 7.3 50.8

π-π* C=0 C-0 C-N

4 5

-285.0/ 0.0 -283.3/+1.7

37.5 3.4

aromatic

1 2 3 4 5

-535.0/-2.5 -533.7/-1.2 -532.5/ 0.0 -530.8/+1.7 -531.8/+0.7

1.6 27.9 50.2 8.5 11.8

1 2 3

-402.7/-1.8 -400.9/ 0.0 -399.2/+1.7

2.1 69.6 28.3

1 2 3 5

-76.8/-4.3 -75.7/-3.2 -74.8/-2.3 -72.5/ 0.0

c-c=o


01s

Nls

A12p

ether carbonyl

imide isoimide

4.0 higher oxidation state 20.3 higher oxidation state 75.7 higher oxidation state 0.0 elemental

Binding Energy (eV)

Fig. 3a: XPS spectra of polyimide with sputter-deposited aluminum: C Is spectrum.



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Binding Energy (eV)

Fig. 3b: XPS spectra of polyimide with sputter-deposited aluminum: Ο Is spectrum.

Binding Energy (eV)

Fig. 3c: XPS spectra of polyimide with sputter-deposited aluminum: Ν Is spectrum.




280

be only s l i g h t changes i n the 01s spectrum (Fig. 3b). However, detailed analysis shows that several new components can now distinguished at lower energies (Peaks 4 and 5) . They can be associated with the appearance of Al-0 species (10,27,30) at the surface. In addition, the Nls spectrum (Fig. 3c) i s now observed to display an important increase i n i n t e n s i t y i n the region corresponding to the appearance of isoimide-like components (peak 3). This suggests a s i g n i f i c a n t modification of the polymer structure. Thus f a r , i t has been f a i r l y obvious that the deposition of sputtered aluminum onto polyimide produces a strong i n t e r a c t i o n between the metal atoms and carbonyl groups. We now see, however, that there i s also evidence of s t r u c t u r a l reorganization at the surface during deposition. This may be due to heat released at the i n t e r f a c e or v i a the i n s e r t i o n of metal atoms into the substrate. The isomerization o f polyimide to isoimide-like structures may help to explain the greatly reduced aromatic character of the polymer at the i n t e r f a c e . The c h a r a c t e r i s t i c chemical s h i f t s observed i n the A12p spectrum (Fig. 4a) indicate that the aluminum deposited on the polyimide now e x i s t s e n t i r e l y as a series of oxidized species at the surface (peaks 1, 2 and 3) s i m i l a r to those already observed by Atanasoska e t a l . (12). on polyimide with low A l coverage (0.5 - 2 À. This agrees with the formation of an Al-O-C complex, presumably i n several d i f f e r e n t environments. A charge d e r e a l i z a t i o n from oxygen to carbon concurrent with reaction i s usually suggested to

"Pr

Binding Energy (eV)

Fig. 4a: XPS spectra of metal electronic core levels present in polyimide treated with sputter-deposited metals: Al 2p spectrum.


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Sputtering ofMetah


«°r

d -92.7

-90.7

-88.7 -86.7 -84.7 Binding Energy (eV)

-82.7

-80.7

Fig. 4b: XPS spectra of metal electronic core levels present in polyimide treated with sputter-deposited metals: Au 4f spectrum.

Binding Energy (eV)

Fig. 4c: XPS spectra of metal electronic core levels present in polyimide treated with sputter-deposited metals: Cu 2p spectrum. 3/2



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explain the absence of an expected 01s chemical s h i f t . No signal from m e t a l l i c aluminum (peak 4) i s observed. The aluminum has thus t o t a l l y reacted with the polymer. This can be explained by the d i f f u s i o n o f the depositing aluminum into the polymer substrate. This has previously been suggested to occur i n t h i s system (27) and i t agrees with findings from nuclear scattering studies which have shown that an extensive penetration of the metal into the bulk occurs (8). GOLD. The deposition o f gold onto polyimide ( F i g . 4b and Table IV) i s also observed to reduce the carbonyl Cls peak i n t e n s i t y (peak 2 of C l s i n Table I I I ) as w e l l as that of the aromatic π - π* C l s (peak 1 of C l s ) , an e f f e c t analogous to that observed f o r the aluminum-polyimide system. New components also appear at lower energies i n the 01s spectrum and there i s an isoimide-like component i n the Nls spectrum (peak 3). Gold i s not generally known to e x i s t i n a stable complex form (marginal chemical r e a c t i v i t y ) and i s Table I I I . Gold on Polyimide

Position/Shift Spectrum Cls

01s

Nls

Au4f / 5

Au4f

2

7 / 2

%Area

Origin

7Γ-7Γ*

Peak

(eV)

1 2 3

-291.7/-6.7 -289.0/-4.0 -286.0/-1.0

0.9 9.3 51.0

4 5

-285.0/ 0.0 -283.4/+1.6

38.0 0.9

1 2 3 4 5

-534.9/-2.4 -533.7/-1.2 -532.5/ 0.0 -531.5/+1.0 -530.4/+2.1

1.6 28.2 54.8 11.1 4.3

1 2 3

-402.7/-1.8 -400.9/ 0.0 -399.4/+1.5

2.5 77.5 19.9

imide isoimide

C=0 C-0 C-N C-C=0 aromatic

_

ether carbonyl

-

_

la 2a 3a

-91.4/-3.1 -89.7/-1.4 -88.3/ 0.0

0.7* 5.9 36.1

+3 +1 elemental

lb 2b 3b

-88.3/-3.7 -86.2/-1.6 -84.6/ 0.0

1.0 7.8 48.5

+3 +1 elemental

*Au4f peak area r a t i o s (5/2:7/2) are expected to be 0.75. They are found to be 0..70 (Au+3), 0.76 (Au+i) and 0.,74 (Auo)


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believed to exhibit poor adhesion with polymers a t room temperature (6). In the gold-polyimide system, the interface i s also generally believed to be free of any measureable chemical interactions (29). Observations by Chauvin et a l . have shown, however, that the adhesive strength of t h i s interface varies with treatment (hydration) (8). Inter f a c i a l intermixing (none occurs with gold) (8) or mixed-phase e f f e c t s cannot account f o r t h i s behaviour. We have observed that s h i f t s i n the various core l e v e l s occur a f t e r the deposition o f gold (low coverage) onto the polyimide surface v i a sputtering. The deposited gold remains mostly i n m e t a l l i c form and does not penetrate into the bulk, i n agreement with nuclear s c a t t e r i n g r e s u l t s (8), but the gold 4 f core l e v e l spectrum ( F i g . 4b) cannot be adequately represented when only peaks of m e t a l l i c gold are used exclusively (peaks 3a and 3b) . Peaks with the chemical s h i f t of A u (peaks 2a and 2b) must also be included i n order to obtain a reasonably s a t i s f a c t o r y f i t . An even better f i t i s obtained by including A u (peaks l a and l b ) . This f i t i s kept consistent with t h e o r e t i c a l 4 f peak area r a t i o s and reported binding energy values f o r A u and A u species (31). I t c l e a r l y indicates that gold i s present a t the interface i n several c h a r a c t e r i s t i c oxidation states (32). This would explain the low energy 01s components (Au-0 species), which cannot be accounted f o r by an electron i n j e c t i o n process at the interface or by random peak s h i f t s (33). In coparison, a s i m i l a r process i s reported to occur with palladium, which, although also considered "unreactive", undergoes some reaction, o x i d i z i n g when sputtered onto polyester (34). COPPER. The deposition of copper on polyimide (Table IV) produces r e s u l t s s i m i l a r to the previous systems. There i s depletion of the carbonyl and π - π* Cls peaks and a s i m i l a r quantity of isoimide component i s produced. In addition, there i s a s i g n i f i c a n t change i n 01s peak i n t e n s i t i e s , including the appearance of low energy components s i m i l a r to the other systems and associated with Cu-0 species (23). The Cu 2 p core l e v e l s (Fig. 4c) show the presence of several oxidation states. Therefore, reactions also occur with copper, despite generally held assumptions of marginal chemical r e a c t i v i t y (15,27,35,36). Most of the copper deposited remains i n the m e t a l l i c state, i n agreement with the nuclear scattering r e s u l t s , which show that d i f f u s i o n into the bulk occurs only upon subsequent heating (8.) .


1 +

3 +

1 +

3 +

3 / 2

CONCLUSIONS A comparison o f changes occuring i n Cls, Nls and 01s core l e v e l spectra f o r the systems examined can be emphasized by overlapping t h e i r area-normalized spectra and reveals i n t e r e s t i n g p a r a l l e l s . The e f f e c t s observed f o r a l l the metals examined i n t h i s study are very s i m i l a r . There i s , i n a l l cases, a loss i n r e l a t i v e i n t e n s i t i e s f o r the π - π* and carbonyl peaks of the Cls spectra ( F i g . 5a). There are also comparable changes occurring at both lower and intermediate binding energies (—287.5 and -283.0 eV). The Nls spectra ( F i g . 5c) show comparable decreases i n imide i n t e n s i t y and increases i n isoimide i n t e n s i t y . Correspondingly, a loss of carbonyl i n t e n s i t i e s i s observed i n the 01s spectra ( F i g . 5b), along with the appearance of the new lower energy peaks which can be associated with the appearance o f metal-oxygen species at the interface (10,


284


Table IV. Copper on Polyimide

Spectrum Cls


01s

Nls

Cu2p / 2 3

ο-293.9

%Area

Origin

-291.4/-6.4 -289.0/-4.0 -286.1/-1.1

1.6 9.5 45.7

4 5

-285.0/0.0 -283.4/+1.6

41.9 1.3

π-π C=0 C-O C-N C-C=0 aromatic

1 2 3 4 5

-535.0/-2.5 -533.7/-1.2 -532.5/ 0.0 -531.6/+0.9 -530.5/+2.0

1.4 27.4 54.3 12.7 4.3

1 2 3

-402.7/-1.8 -400.9/ 0.0 -399.2/+1.7

2.5 79.9 19.9

1 2 3 4

-936.1/-2.7 -934.5/-1.1 -933.4/ 0.0 -931.9/+1.5

0.9 higher oxidation state 16.7 higher oxidation state elemental 74.4 8.0 -

Peak

Position/Shift (eV)

1 2 3

-291.9

-289.9

-287.9

-285.9

_

ether carbonyl

_

imide isoimide

-283.9

-281.9

Binding Energy (eV)

Fig. 5a: Overlapping spectra of non-metallized and metallized polyimide: C Is spectra. 1 = Untreated; 2 = wt. Al; 3 = wt. Au; 4 = wt. Cu.



20. DOMINGUE ET AL.

ο-536.4

-535.2

285

Sputtering ofMetals

-534.0

-532.8

-531.5

-530.3

-529.1

Binding Energy (eV)

Fig. 5b: Overlapping spectra of non-metallized and metallized polyimide: Ο Is spectra. 1 = Untreated; 2 = wt. Al; 3 = wt. Au; 4 = wt. Cu.

ο-404.5

-403.3

-402.0

-400.8

-399.6

-398.4

-397.2

Binding Energy (eV)

Fig. 5c: Overlapping spectra of non-metallized and metallized polyimide: Ν Is spectra. 1 = Untreated; 2 = wt. Al; 3 = wt. Au; 4 = wt. Cu.




286

23,27,30,31). I t seems that, i n a l l cases, the i n i t i a l reaction occurs p r e f e r e n t i a l l y a t the PMDA carbonyl oxygen. Subsequent reactions which may occur at other s i t e s , eg., the PMDA aromatic r i n g , the ODA aromatic r i n g (13), were not observed. There also was no evidence o f any s i g n i f i c a n t metal-carbon bond formation (28) i n these systems. Thus, a v a r i e t y of sputtered metals, including gold, are found to be capable o f reacting with polyimide when deposited at room temperature. In contrast to previous studies of evaporated films which indicate no reactions with gold or copper, the reaction between metal and polymer i s extensive on sputter-deposition due to the greater energies of the m e t a l l i c species under these conditions. The reactions observed occur p r e f e r e n t i a l l y at carbonyl s i t e s , the extents of which vary with the sputtered metal and conditions used. We have seen no evidence of metal reaction a t any other s i t e . The extra energy also produces important changes i n the surface polymer structure including, possibly, the formation of isoimide-like components. ACKNOWLEDGMENTS This research was supported by the Natural Sciences and Engineering Research Council of Canada and both the MESS and the Fonds FCAR du Québec. We thank S. Poulin-Dandurand f o r help with the i n i t i a l data.

LITERATURE CITED 1. 2. 3. 4. 5. 6. 7.

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RECEIVED May 16, 1990


Reaction During the Sputtering of Metals onto Polyimide - ACS

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